The 2 dirtiest parts of the engine bay, from my experience at least, comes from the gap between the front bumper cover and the radiator being open (some manufactures have this open, some don't) as well as the area from the front bumper cover to the frame crossmember being uncovered (again, some manufactures cover this already). My wifes old car was pretty dirty under there, a good majority of the air through the lower grill would easily just get redirected under the car. I used coroplast to make ducting from the grill opening to the sides and bottom of the radiator and blocked off half of the opening and saw a noticable improvement. I then made an under tray/belly pan from the bumper to the crossmember and on the interstate I was getting about 6 mpg more than before, and that was with 4 adults in the car. With the belly pan going back/down to the crossmember there should have been plenty of room for the air to get out, if anything I think it may have even created a low pressure area to help draw air out of the engine compartment.

well, i've noticed an improvement, but i've also noticed the temps go up a lot(though not fast) on hotter days (80+F) and the fans don't kick on until 220F, but when they do the temp drops like a rock until they shut off around 204F. the radiator is damaged and i think that could be the main cause. but all in all i'm satisfied and will look into replacing the radiator prior to making the belly pan permanent

Did you ever get the cooling issues resolved?

I am not a fan of grille blocks because I had some scary moments of near overheating when the weather and or traffic changed plus once a fan controller failure forced me to pull over.

I am not a fan of grille blocks because I had some scary moments of near overheating when the weather and or traffic changed plus once a fan controller failure forced me to pull over.

Not so much due to the grill block, but in general just to direct all the incoming air to the radiator.

The cooling issues got resolved with a new radiator/coolant flush. After pulling the old radiator I back-flushed it and got some nastiness out. The fans would only kick on if stuck in traffic with the new radiator/coolant.

That car is long gone, one day the trans decided it didn't want to disengage the parking pawl when I put it in gear (my best guess anyway). It had been sitting for about a month due to a seized AC compressor so I suspected the brakes were sticking when I tried to back up. Gave it some gas, heard/felt a big clunk, and ended up with trans fluid on the driveway.

One of the main reasons to take air into the front is the radiator. Can you move the radiator to the rear of the car, fan the air from under the rear, through the radiator, and exit it through a new grill between the tail lights, filling in that low pressure area? You can use a much smaller front intake, perhaps a small thermostatically open-able chin intake where you can reduce under-car flow,, to vent the hot engine compartment air out behind the front wheels, where there is a low pressure area.

One of the main reasons to take air into the front is the radiator. Can you move the radiator to the rear of the car, fan the air from under the rear, through the radiator, and exit it between the tail lights, filling in that low pressure area? You can use a much smaller front intake, perhaps a small thermostatically open-able chin intake where you can reduce under-car flow,, to vent the hot engine compartment air out behind the front wheels, where there is a low pressure area.

That's a bag of cats.

Maybe you should find some historic examples of what you are talking about, probably looking in early 1970's racing and read why they may have failed.

Maybe a living example can be found in one of today's race cars.

Someone is going to mention one of the Ford Probe cars, maybe the IV..........let us know what you find.

I personally think radiators like high pressure areas to force air though their gills, lower pressure at the tail end of the car maybe isn't all that attractive from an engineering efficiency standpoint.

Or I can keep it short to save time. drawing the air from under the car is inefficient because of already turbulent airflow. Removing some of it and discharging it out the back isn't going to do any good becuase you're taking turbulent air from 1 area and moving it somewhere else. It would lower the air pressure under the car which will screw with aero on the sides, same way your rear window aero is weird due to air coming from the sides and wrapping around. I imagine there's probably a really good reason why you don't see it on racecars. The only racecars I can really think of that relocate the radiator in any way are some rally cars, where aero is minimally important. Probably the best cars to look at for ideas would be NASCAR racers, since they are required to keep the radiator up front. All the ducting you'd have to run, not to mention the weight of the fans to pull the air up is just going to be extra weight that's going to make the air leaving the car turbulent as heck.

I've always imagined that the front of the car is kind of like a parachute when it comes to drag. I think that adding hood vents to a car would have a measurable gain in fuel economy, but I have yet to obtain hood vents to try this.